CD133 is utilized as a marker for tumor-initiating cells of glioma, but its physiological function is still not well understood. To dissect the function of CD133, we tried to identify CD133-binding proteins, using pull-down methods, immunoprecipitation assays, and yeast two-hybrid techniques. On the other hand, we found that in human embryonic carcinoma NTERA-2 cells, CD133 suppresses the expression of Epithelial Splicing Regulatory Protein 1 (ESRP1), an RNA splicing factor that regulates epithelial-mesenchymal transition (EMT).